The most famous use of this phrase was by Lord Mansfield in 1772 when he was passing judgement in court and freed an imprisoned slave.

"The constitution does not allow reasons of state to influence our judgment. God forbid it should! We must not regard political consequences, however formidable they might be; if rebellion was the certain consequence, we are bound to say, 'Justitia fiat, ruat coelum'."

As such, this motto has become the founding principle of jurisprudence. Reminding us all that Justice is the most important function of the law and of our legal systems, if the law does not provide justice then the law must be changed (thus our system (in the US and UK) of legal precendents making the legal system a dynamic, living entity).